Hydraulic shock absorber for a motor vehicle having flow control valving that becomes more restrictive during the service life of the shock absorber

ABSTRACT

A shock absorber for a motor vehicle suspension includes a piston construction having flow control valving that becomes more restrictive during the life of the shock absorber to compensate for the reduction in friction damping in the suspension during usage. The piston valving includes a flow passage surrounded at one of its ends by an annular land that forms a valve seat. A valve element is urged to a closed position against the seat by the cumulative force of a primary spring and a secondary spring. The secondary spring provides a spring force countering the force of the primary spring but is constructed to progressively take a permanent set after repeated cycling whereby the cumulative force of the two springs urging the valve element to a seated condition will increase during the service life of the shock absorber.

BACKGROUND OF THE DISCLOSURE

The present invention relates to hydraulic shock absorbers for a motorvehicle suspension, and more particularly to a shock absorberconstructed to become progressively stiffer during its service life.

In a conventional automotive suspension system, jounce and reboundmovement is damped both by the friction in the system and by a hydraulicshock absorber. During repeated cycling of the suspension system, therewill be a lessening of the friction in the various pivots and othercomponents of the suspension due to wear and, consequently, aprogressive reduction in friction damping. In order to compensate forchanges in the friction damping characteristics of a vehicle suspensionduring its service life, it is an object of the present invention toprovide a shock absorber that becomes progressively stiffer andincreases its damping ability during its service life.

BRIEF SUMMARY OF THE DISCLOSURE

In accordance with the presently preferred embodiment of this invention,a hydraulic shock absorber for a motor vehicle has a pressure tube inwhich a piston is reciprocably mounted. The pressure tube is connectedto an unsprung component of the vehicle suspension and the piston isconnected by a piston rod to a sprung component such as a vehicle bodyor frame member.

The shock absorber piston divides the pressure tube into jounce andrebound pressure chambers and has jounce and rebound flow controlpassages. The passages permit the restricted flow of fluid between thepressure chambers for the purpose of damping relative movement of thesuspension components.

An annular land forms a valve seat at one end of the piston andsurrounds one end of one of the flow control passages. A valve elementis pushed toward a seated condition against the valve seat by acomposite spring construction. The composite spring includes a primarycoil spring which urges the valve element toward a seated position. Asecondary spring of the Belleville type engages the end of the coilspring and exerts a spring force which tends to counteract the force ofthe coil spring. Thus, the total force urging the valve element to aseated condition is the cumulative force of the primary and secondarysprings.

The Belleville secondary spring is made out of aluminum rather thanconventional hard spring steel. It is designed to progressively lose itsspring force upon repeated flexing which occurs during the cycling ofthe shock absorber in the vehicle. When the secondary spring loses itsspring force, the cumulative or total force of the primary and secondarysprings urging the valve element to a seated condition increases. Anincrease in cumulative spring force produces a corresponding increase inthe restriction to the flow of fluid through the flow control passage.In a vehicle suspension where the frictional damping of the suspensioncomponents decreases during usage the present shock absorber willcompensate for such loss of friction damping by becoming stiffer as thesecondary Belleville bell spring loses its resiliency.

BRIEF SUMMARY OF THE DRAWINGS

The many objects and advantages of a shock absorber in accordance withthe present invention will become apparent upon consideration of thefollowing discussion and the accompanying drawings, in which:

FIG. 1 is an elevational sectional view of a hydraulic shock absorberfor a motor vehicle in accordance with this invention;

FIG. 2 is an enlarged sectional view of the piston construction of theshock absorber of FIG. 1;

FIG. 3 is an elevational view of the piston rod, the piston rod sealstructure and an exploded view, in section, of the piston;

FIG. 4 is a plan view of the jounce valve element;

FIG. 5 is a sectional view taken along section line 5--5 of FIG. 4 of aportion of the jounce valve element;

FIG. 6 is a plan view of the rebound valve element;

FIG. 7 is a sectional view taken along section line 7--7 of FIG. 6 ofthe rebound valve element;

FIG. 8 is a plan view of the secondary rebound valve spring; and

FIG. 9 is a sectional view taken along section line 9--9 of FIG. 8 ofthe secondary rebound valve spring.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings, wherein the presently preferredembodiment of this invention is illustrated, FIG. 1 shows a hydraulicshock absorber for use in a motor vehicle for the purpose of dampingjounce and rebound movement of vehicle suspension components. The shockabsorber 10 includes a pressure tube 12 that is closed at its lower endby a foot valve assembly 14. A piston assembly 16 is slidably disposedwithin the pressure tube 10. A piston rod 18 has its lower end connectedto the piston assembly 16 and extends upwardly out of the shockabsorber. An annular piston rod guide 20 slidably supports the pistonrod 18 and closes the upper end of the pressure tube 12. The pistonassembly 16 divides the interior of the pressure tube into rebound andjounce pressure chambers 22 and 24.

A reservoir tube 26 is concentrically disposed about the pressure tube12 and forms an annular reservoir chamber 28 therewith. The lower end ofthe reservoir tube 26 is closed by a closure member 30 having agenerally cup shape and circumferentially spaced apart raised portions32 that engage the foot valve assembly 14. The closure member 30,including its raised portions 32, maintains tube 26 concentric withrespect to the pressure tube 12. The spaces between the raised portions32 provide communication between the reservoir chamber 28 and the area34 situated directly beneath the foot valve assembly 14.

The rod guide 20 has a cylindrical upper portion 36 upon which a cupshape upper closure member 38 is seated. The closure member 38 has adepending flange portion that is in rigid sealed engagement with theupper end of the reservoir tube 26. As seen in the drawings, the guide20 in addition to slidably positioning the piston rod 18 also maintainsthe reservoir tube 26 concentric with respect to the pressure tube 12. Arubber sealing element 42 of annular configuration surrounds the pistonrod 18 and is urged upwardly against the closure member 38 by means of acoil spring 44 that is interposed between the piston rod guide 20 and awasher 46 that bears against the seal 42. A passage 48 is provided inthe rod guide 20 to permit fluid escaping from the rebound chamber 22 toflow back to the reservoir chamber 28. With this construction, the seal42 is not subjected to the high hydraulic pressures that are present inthe rebound chamber 22 during the operation of the shock absorber.

Referring to FIG. 2, the piston assembly 16 includes a piston element 50having a circumferentially arranged series of rebound passages 52 formedtherein. The element 50 also includes a circumferential series of jouncepassages 54 that are spaced outwardly from the rebound passages 52. Onthe rebound pressure chamber side of the piston element 50, inner andouter annular lands 55 and 56 surround the jounce passages 54. A jouncevalve element 57 (the construction of which will be described in greaterdetail later) engages the valve seats 55 and 56 formed by the inner andouter lands and is urged to a seated condition by star shape valvespring 58. A washer shape member 59 engages a shoulder 61 formed on thepiston rod 18 and engages the hub of the star shape spring 58.

On the jounce chamber side of the piston element 50, an annular land 62surrounds the rebound passages 52. A rebound valve element 63 (theconstruction of which will be described in greater detail later) isseated against the valve seat formed by the land 62. The rebound valveelement 63 is held against its valve seat 62 by the cumulative force ofprimary and secondary valve springs. A Belleville spring 64 constitutesthe secondary spring and is positioned against the rebound valve element63 and exerts a spring force upon an annular valve seat 66. A nut 67threadedly engages the end of the piston rod 18 and has an outwardlyextending flange 68 that forms another spring seat. A coil spring 69,which constitutes the primary valve spring, is interposed between theflange 68 of the nut and the annular valve seat 66.

The tightening of the nut 67 secures the various valve elements andvalve springs and the piston body to the end of the piston rod 18.

Referring to FIGS. 4 and 5, the jounce valve element 57 has a generallycircular outer portion 71 and a generally circular inner portion 72 thatis spaced apart from the outer portion 71. The hole 70 defined by thecircular portion 72 accommodates the end of the piston rod 18. Theportions 71 and 72 are joined by an interconnecting portion 73. Thecrescent shape space formed between the outer and inner portions 71 and72 is aligned with the upper end of the rebound passages 52 so as not tointerfer with the flow of fluid therethrough.

The jounce valve element 57 has a thin spring metal backing 74 to whichan organic facing material 75 is bonded. The facing 75 is provided witha diametrical gap 76 that exposes the surface of the metal backing 74.

The organic facing may be made of a suitable polyamide resin such asnylon. Other resins having the desired plastic deformabilitycharacteristics may also be used. A compound of rubber would make aneffective organic facing.

When the jounce valve element 57 is properly positioned in the pistonassembly 16, the organic facing 75 engages the annular valve seats 55and 56. Due to the presence of the gap 76 in the facing material 75,restrictive orifices are defined by the gap 76, the metal backing 74 andthe valve seats 55 and 56.

The rebound valve element 63 is of generally annular shape and has aspring metal backing portion 78. The hole 77 in the center of the valveelement 63 accommodates the end of the piston rod 18. An organicmaterial facing 79 is bonded to the surface of the metal 78. The organicfacing 79 is provided with spaced edges that define a diametricallyarranged gap 81. The material of the facing 79 is the same as thematerial 75 of the jounce valve element 57. When the rebound valveelement 63 is positioned against the lower side of the piston 50, theorganic facing 79 engages the annular valve seat 62.

The gap 81 cooperates with the valve seat 62 to form restrictive floworifices each having one dimension equal to the thickness of the facing79. The organic facing 79 holds the surface of the metal backing 78spaced apart from the valve seat 62 and the gap 81 in the facing 79provides restrictive orifices through which fluid may flow.

OPERATION

The hydraulic shock absorber 10 illustrated in the drawing isconstructed to be interposed between the sprung and unsprung members ofa vehicle suspension system. The upper end of the piston rod is designedto be connected to a sprung vehicle component such as a frame or bodymember. The lower end of the closure member 30 is constructed to beconnected to an unsprung suspension component such as a suspension arm.

When the shock absorber 10 is interposed between the sprung and unsprungsuspension components of a motor vehicle, the piston assembly 16 willreciprocate within the pressure tube 12 during jounce and reboundmovement of the suspension. The shock absorber 10 is filled withhydraulic fluid and as the piston 16 moves within the pressure tube 12,fluid will be forced through the several restrictive orifices to dampenthe jounce and rebound movement.

During a jounce stroke, the piston 16 will move downwardly. Fluid willflow from the jounce chamber 24 to the rebound chamber 22 through thejounce passages 54 and through the restrictive orifices formed by thegap 76 in the organic facing 75 of the jounce valve element 57. Fluidwill also flow from the jounce chamber 24 to the rebound chamber 22through the restrictive orifices formed by the gap 81 in the organicfacing 79 of the rebound valve element 63. If the pressure in the jouncechamber 24 is sufficiently high, the jounce valve element 57 will moveto an open position against the force of the star shape spring 58whereby the organic facing 75 will be spaced apart from the annularvalve seats 55 and 57. This will permit the escape of hydraulic fluidfrom the jounce chamber 54 to the rebound chamber 52. When the pressureceases the spring 58 will cause the valve element 57 to snap back intoengagement with the annular valve seats 55 and 56.

Upon repeated cycling of the shock absorber and the repeated movement ofthe jounce valve element 57 from an open to a seated position, plasticdeformation of the organic facing 75 will occur. Progressively andgradually during usage of the shock absorber 10, the pounding of thevalve element 57 against the valve seats 55 and 56 will cause creases orgrooves to be formed in the organic facing 75. As these grooves areformed, the depth of the gap 76 will decrease whereby the size of therestrictive orifices formed by the gap 76 (in association with the valveseats 55 and 56) will be decreased whereby the restriction to fluid flowthrough the jounce passages 54 will be increased gradually andprogressively during the service life of the shock absorber.

During a rebound stroke, when the piston 16 is moving upwardly in thepressure tube 12, fluid will flow through the rebound passages 52,through the restrictive orifices formed by the gap 81 in the organicfacing 79 of the rebound valve element 63. Fluid will also flow from therebound chamber 22 to the jounce chamber 24 through the jounce passages54 as permitted by the restrictive orifices formed by the gap 76 in theorganic facing 75 of the jounce valve element 57.

During a rebound stroke the pressure in the rebound chamber 22 willcause the valve element 63 to move out of engagement with the valve seat62 against the cumulative force of the Belleville spring 62 and the coilspring 69. When the fluid pressure is relieved, the rebound valveelement 63 will snap back into engagement with the valve seat 62. Duringthe service life of the shock absorber 10, the repeated contact of theorganic facing 79 with the annular land 62 will cause a groove to beformed in the organic facing. The material of the facing 79 will beplastically deformed progressively and gradually during the life of theshock absorber so that the size of the restrictive orifices formed bythe gap 81 will be progressively and gradually decreased.

By way of example, the organic facings 75 and 79 may have a thickness inthe range of 0.0020 to 0.0035 inch. One dimension of each orifice formedby the gaps 76 and 81 in the facings 75 and 79 will be equal to thethickness of the facing where it is in contact with the respective valveseat. Initially, that dimension will be 0.0020 to 0.0035 (or whateverthickness the facing has), however, after continual opening and closingof the valve elements and the formation of grooves in the facings 75 and79 by the valve seats, that dimension of the orifices will graduallyapproach zero.

Thus, during the service life of the shock absorber 10, the restrictiveorifices formed by gap 81 in the organic facing 79 of rebound valveelement 63 and the restrictive orifices formed by the gap 76 in thefacing 75 of the jounce valve 57 will gradually and progressively bereduced in size. As a consequence, the shock absorber 10 will becomeprogressively stiffer during its service life with respect to bothjounce and rebound movement.

The rebound valve element 63 moves off of the valve seat 62 during arebound stroke against the cumulative force exerted by the Bellevillespring 64 and the coil spring 69. The spring 69 is a primary springexerting a dominant force urging the rebound valve element 63 to aseated condition. The Belleville spring 64 is a secondary spring andexerts a force tending to counteract the force of the coil spring 69.Thus, the total force exerted by the two springs urging the valve 63against its seat is less than the force exerted by the coil spring 69alone. During the service life of a shock absorber, the Belleville valvespring 64 will be repeatedly flexed. This spring is formed of aluminumor similar material and repeated flexture will cause a permanent set toprogressively take place in the spring. That is, the spring forceresisting the coil spring 69 will progressively and gradually decreaseduring the service life of the shock absorber 10. With a reduction incounteracting force, the total force or cumulative force of the twosprings 64 and 69 urging the valve 63 against its seat willprogressively and gradually increase during the service life of a shockabsorber. An increase in the cumulative force urging the rebound valveelement 63 to a seated position will result in the shock absorber 10being more resistant to rebound movement and, therefore, having thecapacity to compensate for any loss of friction damping in thesuspension.

An annular fatigue groove 82 may be provided in the Belleville spring 64to enhance the ability of the spring 64 to lose its resiliency andcounteracting force.

The organic facings for the jounce and rebound valve elements 57 and 63may be formed of nylon or rubber. It will be appreciated that otherorganic materials that are subject to plastic deformation in response torepeated pounding by a valve seat are also acceptable.

The foot valve 14 is similar in construction and operation to the footvalve described in U.S. Pat. No. 2,691,387 to J. N. Strauss. During acompression stroke when the piston assembly 16 is travelling downwardlyin the pressure tube 12, the jounce chamber 24 will be reduced in size.Fluid will flow from the jounce chamber 24 through the valving of thefoot valve 14 to the reservoir chamber 28 in an amount equal to thefluid displaced by the piston rod 18. During a rebound stroke when thepiston assembly 16 is moving upwardly in the pressure tube 12, fluidwill be drawn through the replenishing valve passages of the foot valveassembly 14 into the jounce chamber 24 from the reservoir chamber 28 inan amount equal to that which was displaced by the piston rod 18 as itis withdrawn from the pressure tube 12.

A shock absorber in accordance with this disclosure will becomeprogressively stiffer during usage whereby the reduction in frictiondamping that occurs during the service life of a vehicle suspensionsystem will be compensated for.

The foregoing description presents the presently preferred embodiment ofthis invention. Modifications and alterations may occur to those skilledin the art that will come within the scope and spirit of the followingclaims.

I claim:
 1. A hydraulic shock absorber constructed to become stifferduring usage having first and second fluid chambers and flow controlmeans constructed to provide a restictive fluid passage for thecontrolled flow of hydraulic fluid from said first chamber to saidsecond chamber;said flow control means including a fluid passage, avalve seat positioned about one end of said passage and a valve element;spring means exerting a cumulative spring force upon said valve elementurging said valve element into seated engagement with said valve seat;said spring means comprising a primary spring exerting a spring forceurging said valve element toward said seated position and a secondaryspring exerting a spring force tending to counter the force of saidprimary spring on said valve element; said secondary spring having aservice life substantially less than the service of said primary springwhereby the cumulative force of said primary spring and said secondaryspring increases during the service life of said shock absorber;saidsecondary spring comprising a Belleville spring having an annularfatigue groove constructed to cause said spring force exerted by saidsecondary spring to be substantially reduced during repeated flexing ofsaid secondary spring.
 2. A hydraulic shock absorber constructed tobecome stiffer during usage having first and second fluid chambers andflow control means constructed to provide a restrictive fluid passagefor the controlled flow of hydraulic fluid from said first chamber tosaid second chamber;said flow control means including a fluid passage, avalve seat positioned about one end of said passage and a valve element;spring means exerting a cumulative spring force upon said valve elementurging said valve element into seated engagement with said valve seat;said spring means comprising a primary spring exerting a spring forceurging said valve element toward said seated position and a secondaryspring exerting a spring force tending to counter the force of saidprimary spring on said valve element; said secondary spring having aservice life substantially less than the service of said primary springwhereby the cumulative force of said primary spring and said secondaryspring increases during the service life of said shock absorber; saidprimary spring comprising a coil spring manufactured from hardenedspring steel material; said secondary spring comprising a Bellevillespring manufactured from a material that is less hard than the materialof said primary spring; said secondary spring having an annular fatiguegroove constructed to cause the spring force exerted by said secondaryspring to be substantially reduced during repeated flexing of saidspring.
 3. A hydraulic shock absorber for a motor vehicle suspensionhaving a sprung vehicle component and an unsprung vehicle component;saidshock absorber having a pressure tube; a piston slidable within saidpressure tube dividing the interior of said tube into jounce and reboundfluid pressure chambers; said piston being constructed to be connectedto one of said components and said pressure tube being constructed to beconnected to the other of said components; said piston having fluidpassage means constructed for the controlled flow of hydraulic fluidfrom one of said chambers to the other of said chambers; said pistonhaving an annular valve seat positioned about one end of said passagemeans; a valve element and spring means urging said valve element intoseated engagement with said valve seat; said spring means comprising aprimary spring exerting a spring force urging said valve element towardsaid seated position and a secondary spring exerting a spring forcetending to resist the force of said primary spring on said valveelement; said second spring having a service life substantially lessthan the service of said primary spring and said secondary springincreases during the service life of said shock absorber; said primaryspring comprising a coil spring manufactured from hardened spring steelmaterial; said secondary spring comprising a Belleville springmanufactured from a material that is less hard than the material of saidprimary spring; said secondary spring having an annular fatigue grooveconstructed to cause the spring force exerted by said secondary springto be substantially reduced during repeated flexing of said spring.